In installations for reprocessing irradiated fuels, the fuel elements issuing from the reactors are stored in a pond, cut in shears and the pieces obtained are dissolved.
A fuel element comprises two so-called end-pieces made of metal which imprison the ends of the pencils, the latter contain the fuel but are bereft thereof over a small length at their ends.
The length and section of the element may vary; it depends on the type of reactor from which the element issues. In PWR's, the elements have sections of the order of 270 mm.sup.2 ; in BWR's, of the order of 120 mm.sup.2. The BWR elements are slightly shorter than the PWR elements.
The element having left the storage pond is placed in a magazine adaptable to the shearing device. The magazine generally has a rectangular or square section (adapted to the shape of the element); it is formed by non-mobile metal walls. Forward or rearward displacement of the element in the magazine is obtained by means of a pusher combined with a so-called drive element. The pusher acts on a so-called head endpiece of the element.
This pusher makes it possible to advance the element towards the blade of the shears, and, if it is provided with grab means, to cause it to move backwards. The drive device gives the force of thrust (or of reverse travel) applied to the pusher; this may, for example, be a jack, a pusher chain, or the like.
The dimensions of the magazine have consequences on the arrangement and dimensions of the holding down clamps (holding pads) in particular which are placed at the free end of the magazine and which compress the element to be sheared. Consequently, when it is desired to pass from one type of element to another, the clamps and other relevant pieces of the shears must first be replaced. This operation is effected by remote control (the prevailing radio-activity prohibiting access to human beings) and by means of a lifting bridge handling a beam on which the pieces to be changed are fixed.
When passing from elements of large dimensions (PWR) to elements of smaller dimensions (BWR), it might be envisaged to conserve the same magazine in order to avoid the operations described hereinabove.
However, in that case, the cuts at the end of the elements raise problems. This state of the art is illustrated in FIGS. 1 and 2 of the accompanying drawings.
FIGS. 1 and 2 show the end of cut on a BWR element in a magazine for PWR elements, not provided with the device according to the invention. (FIGS. 3 to 8 show the device according to the invention).
According to FIG. 1 (view in elevation), the fuel element 1 of small dimensions (BWR) with its endpiece 2 and its pencils 3 is disposed in a magazine 4 whose dimensions correspond to those of the elements of larger dimensions. The pusher 5 formed by metal walls has substantially the section and depth of an endpiece of PWR element. It may thus imprison the endpiece of the PWR element, but it does not maintain the endpiece of the smaller BWR element.
In FIGS. 1 and 2, inserts are placed in the pusher so as to maintain the head endpiece 2 fixed and to ensure a controlled thrust under the action of a pusher chain 10.
In order to be cut, the element is placed horizontally; it abuts on the lower part 6 of the magazine (FIG. 1 in elevation) and on wall 7 of the magazine corresponding to the counter-blade (FIG. 2 in plan view). This wall 7 is the one located opposite the action of the holding clamps 8 and 9 (holding pads).
For cutting, the principal clamp 9 compresses the pencils so as to render them contiguous, the auxiliary clamp 8 by its action maintains their curvature regular.
When cutting comes to an end, the auxiliary clamp 8 must be withdrawn so as to allow cut of the pencils near the endpiece; by way of indication, about 500 mm of pencil remain.
Reverse movement of this clamp 8 leaves between the pusher 5 and said clamp a recess in which the pencils still in place which have been subjected to actions of deformation during cut of the element, are blocked and break. This phenomenon is illustrated in FIG. 2.
Moreover, as shown in FIG. 1, vertical expansion of the pencils being free (the section of the magazine is larger than that of the element and the clamps compress pencils in the horizontal direction), breakage of the pencils at the level of endpiece 2 is promoted.
During the opening of the clamp 9 necessary for the advance of the element, the free pencils 11 may tip over and obturate the spout supplying the dissolver (not shown).